WoD is objectively the worst expansion as it did pretty much everything wrong from a MMO design perspective, but with good intentions.
Following the feedback from MoP it wasn't very surprising, though.
Give us choices!
Nothing should be mandatory!
Just let us raid then do what we want!
Factions should reward cosmetics, no pre-raid gear!
Daily quests are the worst thing ever!
We don't want to cap Valor or a currency every week or we fall behind!
Grinding mats for professions suck!
Coupled with Garrisons which could probably fair pretty well in any other expansion (Order Halls are doing great in part because you have other ways to progress too), WoD became the epitome of 'giving players what they think they want until they get it'. Apathy after 2 weeks of 6.0 even for casuals (after doing Highmaul, prepared your Garrison, you just looked around and asked 'Well, now what?'. Then came 6.1 which was an insult, and 6.2/Tanaan that in panic tried to remedy the situation of the mass exodus due to players literally having fuck-all to do after they've done their weekly raid. I can't think of any period in the game I had less things to do as a non-raider.
Sometimes it feels like the only people that ever defended WoD, was the armchair-pretend-hardcores that thought that they had suddenly become pros at the game because WoD allowed you to raid at that level since the only thing that mattered was weekly clears. If you can raid Mythic and still only play 6-7 hours a week in total you can bet your ass everyone else is bored to tears.
Legion is far from flawless, but it's still doing most things right. Just sad to see that culture shock from WoD made people think they should be able to 'cap' their characters in a couple of hours every week.